The invention relates to an additional, friction-wheel-driven grinding spindle for bevelling the edges of spectacle lenses on a spectacle-lens-edging machine. The machine has two coaxial half-shafts for retaining and rotating a spectacle lens. It has a grinding spindle with an axis parallel to the half-shafts. The spindle can be moved radially and axially, along with the bearing housing that supports the spindle, relative to the half-shafts. The spindle carries a rough grinding and finish grinding wheel for grinding the spectacle lens periphery, and it optionally has a groove for grinding a ridge bevel.
A conical grinding tool arranged on the bearing housing follows the radial and axial movements of the bearing housing relative to the half-shafts supporting the spectacle lens. The tool rotates around an axis extending radially with respect to the spectacle lens. The grinding tool is intended for bevelling the edges of the spectacle lens periphery and is driven by the grinding spindle, via an angular drive which comprises a pair of friction wheels. The angular drive comprises a first friction wheel, which is positioned on a neck of the bearing housing, and a second friction wheel, which is seated on the work spindle, that bears the conical grinding tool and is mounted in a further bearing housing perpendicularly with respect to the grinding spindle.
A spectacle lens-edging machine of the above type is described in U.S. Pat. No. 5,363,597. This machine has proven successful, in particular, for providing grooves or scores in the region of the periphery of the ground-to-shape spectacle lens. For providing grooves or scores, the radial machining tool is moved in a controlled manner both axially and radially with respect to the spectacle lens. This can be carried out purely mechanically or by means of CNC control, wherein the computer also controls the grinding in accordance with a predetermined spectacle lens periphery.
In this known spectacle lens-edging machine, the angular drive is always in drive connection with the grinding spindle. As a result, the work spindle with the machining tool runs at high speed along with the grinding spindle and, accordingly, is subjected to an unnecessarily high degree of wear.
If only a slight bevel is desired to remove the sharp edge which has been produced during the grinding operation from the periphery of the ground-to-shape spectacle lens, then there is no need either for the radial machining tool to run constantly with the grinding spindle or for controlled guidance of the machining tool in the axial direction of the spectacle lens.
U.S. Pat. No. 5,056,270 discloses a spectacle lens-edging machine having two coaxial half-shafts for retaining and rotating a spectacle lens. A grinding spindle is arranged with its axis parallel to the half-shafts. The spindle can be moved radially and axially, with its bearing housing, relative to the half-shafts. The machine has a rough grinding and a finish grinding spindle for grinding the spectacle lens periphery. It has a grinding wheel with a groove for grinding a ridge bevel. The wheel has a grinding tool which rotates around an axis running essentially radially with respect to the spectacle lens and is intended for bevelling the edges of the spectacle lens periphery. The grinding tool is driven by a motor and is arranged in an axially displaceable manner on a retaining means which is itself fastened on a slide. The slide, in turn, can be pivoted around an axis. The slide is mounted on a retaining means which is fastened on the bearing housing for the half-shafts such that it can be displaced parallel to the half-shafts.
The grinding tool provides a safety bevel on the ground periphery spectacle lens. For this purpose, it has its own control means, to cause both the axial displacement of the grinding tool and the axis parallel displacement of the slide in order to bring the grinding tool into engagement with the edges of the spectacle lens periphery. This known apparatus is complicated because, in addition to the control means for the radial and axial movement of the spectacle lens relative to the grinding wheels, it is also necessary to have a further control means for moving the additional grinding tool once grinding of the spectacle lens periphery has been completed.